The Braille language is the universally accepted form of written communication for the visually impaired. It utilizes a system of dots arrayed in a three row by two column grid. Raised dots are located in any combination of the six positions in the grid, to display different letters, numbers, and symbols based on the configuration of the raised dots. Worldwide, the Braille system provides millions of visually impaired individuals with a method for reading and writing.
For this method of communication to be accurate and precise, universal specifications have been developed. Each dot has a base diameter of 1.44 millimeters (0.057 in.) while being 0.48 millimeters (0.019 in.) in height. Within each individual grid, the dots are 2.34 millimeters (0.092 in.) apart, measured center-to-center, and each individual character is of 6.22 millimeters (0.245 in.) away from the neighboring character.
The distance between two Braille pins is at least 2.34 millimeters apart because this is the minimal distance required to distinguish between two points with the fingertip. This minimal distance is determined by mechanoreceptors located on the skin, which are activated by the slightest deformation of the skin due to contact. To discriminate between two points, there must be a deactivated receptor located between two activated receptors. Without the presence of a deactivated receptor, the brain would perceive the contact of the two points as one stimulus.
No device yet exists that allows the visually impaired to read the time in Braille. To tell time, the visually impaired currently rely on either talking or tactile watches. Talking watches function by verbally relaying the time to the user whenever the user presses a button. This method is effective in communicating the time; however, it can be disruptive to others and draws attention to the user. Tactile watches, on the other hand, are silent. They function much like traditional analog watches, except the user touches the face of the watch to feel where the hands are located. There are also raised markings on the tactile watch that indicate the positions of the numbers; however, there is no standard format for these markings and they vary from product to product. Tactile watches can be difficult to read. Also, the hands of tactile watches are exposed while the user is telling the time, and therefore they can be easily broken or damaged. Thus, talking watches are disruptive, while tactile watches are difficult to read and fragile.